Ring formation in Stipagrostis obtusa in the arid north-eastern Negev, Israel

In drylands, particularly in sandy environments, clonal plants occasionally develop into ring patterns that slowly expand radially, leaving bare soil in the ring's center. Several mechanisms have been suggested to explain ring formation, and yet it is very difficult to find out the dominant driving mechanism for each specific ecosystem. This study is the first to assess the rings of Stipagrostis obtusa in the north-eastern Negev of Israel, an arid region with mean annual precipitation of & AP;65 mm. Our results propose that S. obtusa rings form in response to the infiltration feedback, which is enhanced by microtopography; the rings developed on small mounds due to continuous deposition of sand and dust. The infiltration feedback is caused by the sharp contrast in water infiltrability between the rings and the inter-ring spaces, where infiltration is lower. In addition, during heavy rainstorms, runoff generated in the inter-ring spaces partially percolates in the rings' periphery and enhances radial expansion. These source-sink relations increase water availability for the S. obtusa plants, increasing their resilience to the harsh dryland conditions.

Automated summary

In drylands, clonal plants can form ring patterns in sandy environments, which expand gradually and leave bare soil in the center. The formation of these rings is driven by the infiltration feedback, which is enhanced by microtopography. The S. obtusa rings in the north-eastern Negev of Israel are formed on small mounds due to continuous deposition of sand and dust and have higher water infiltrability compared to the inter-ring spaces. During heavy rainstorms, runoff partially percolates in the rings' periphery, promoting radial expansion and increasing water availability for the S. obtusa plants.